The present invention relates to optical resonators, and particularly to fiber optic resonators.
Optical resonators typically comprise a pair of parallel, dielectric mirrors, separated by a small distance. Light incident on the mirrors makes multiple reflections therebetween, with a portion of the light escaping from between the mirrors on each reflection. The escaping light will interfere constructively and destructively, forming a fringe pattern. By analyzing the fringe pattern, the spectral content of the incident light may be ascertained, and thus, the resonator may function as a spectrum analyzer.
The free spectral range (i.e., the difference between resonant frequencies) of such a resonator is inversely proportional to twice the distance between the mirrors. However, because of problems associated with aligning the mirrors at large distances, the free spectral range is usually relatively large. For example, if the mirrors are separated by 1 meter, the free spectral range would be about 1500 MHz. Such a large free spectral range makes it difficult to distinguish frequency spectrum components which have small frequency separations.
In another type of resonator, the resonant cavity is formed from both fiber optic and optic components (e.g., mirrors or beam splitters coupled to a length of optical fiber). However, these hybrid devices also suffer from alignment problems. Further, the round trip losses of light circulating in the resonant cavity are quite high, resulting in a relatively low finesse.